add OpenBSD libc as a cross compilation target

[andrewrk]

Extracted from #514.

This is needed for OpenBSD to become a tier 1 target.

The example set by glibc can be followed.

See also this wiki page: https://github.com/ziglang/zig/wiki/Updating-libc

[norcalli]

@andrewrk is that link broken? It leads to a "create new page" for me.

[redj]

Is this the right wiki page? https://github.com/ziglang/zig/wiki/Updating-libc

same issue in : #2877 (NetBSD) and #2878 (OpenBSD)

[daurnimator]

I fixed the link in andrew's comment.

[iacore]

What should I do to add OpenBSD libc? This project can fetch openbsd libc files.

[semarie]

@locriacyber, openbsd-ziglibc is getting real libc and headers files. I think what is expected here is to get only functions stubs.

[iacore]

not header files? openbsd use clang as the compiler and I think it has its own libc headers. Given how OpenBSD has no ABI guarantee, every version of OpenBSD has its own libc.a libc.so to link with.

[semarie]

to build C program (using zig compiler), you need both (libc stubs and header files). to build ZIG program (using zig compiler), you need only libc stubs (assuming no C dependency).

openbsd-ziglibc extracts the whole sets of C headers which are normally installed (~50 Mo for only one OS version and only one architecture).

(and not all architectures are using clang as compiler, but it is another discussion)

[iacore]

What do you mean by "libc stubs" in case of OpenBSD? The symbol table of libc?

[alexrp]

Just stating for the record that, while I will be tackling both #2876 and #2877, it's very unlikely that I'll work on this one. As far as I can tell, OpenBSD has no support whatsoever for building on anything but OpenBSD; on the other hand, I was able to cross-compile both FreeBSD and NetBSD on Linux.

If an OpenBSD user wants to tackle this, however, I'm happy to help with everything but actually building libc.

[semarie]

just for reference, at some point I was able to cross compile from Linux (I have not check if it is still working). see https://github.com/semarie/openbsd-ziglibc

it is a shell script (runnable on Linux after few modification), which will download objects/libs files from openbsd server, and create a environment suitable for ZIG_LIBC.

[alexrp]

The reason we need to build from source is that, in a release tarball/image, it is nearly impossible to separate the kernel + libc headers from all the other headers coming from various libraries.